The Minister also said that Mr Quaedvlieg, who was sacked for helping his girlfriend get a job within the agency, was "discredited and disgraced".

"He was a man who had groomed a girl 30 years younger than himself. He is discredited and disgraced," Mr Dutton told Parliament on Tuesday. Mr Dutton has previously accused Mr Quaedvlieg of having mental health issues.

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But Mr Morrison has backed his minister, telling ABC's 7.30 that he was disappointed Mr Qaedvlieg had "sought to sledge" Mr Dutton's character.

"I worked with Roman when I was the immigration and border protection minister and I'm disappointed that the claims he's making now have been so palpably demonstrated to be false, I mean they lack complete credibility," he said.

"I then heard the PM on the ABC endorsing that sledging. I’ve written to the Speaker - this is not what privilege is for."

"Grooming? Are you serious? That has a legislative meaning. Is that what he meant? Parliamentary privilege huh."

The war of words between the minister and his former departmental head began over Mr Dutton's use of his ministerial discretion to grant visas for au pairs who were held at the border.

Mr Dutton has used this power thousands of times to step in, often at the request of Labor MPs, but the Opposition argues the au pair cases should be scrutinised because they were for the benefit of Mr Dutton's friends.

Mr Quaedvlieg has given evidence to a parliamentary committee examining the visas.

Latika Bourke is a reporter for The Sydney Morning Herald and The Age based in London. She has previously worked for Fairfax Media, the ABC and 2UE in Canberra. Latika won the Walkley Award for Young Australian Journalist of the Year in 2010.